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Quasi-geostrophic dynamics in the presence of moisture gradients

Monteiro, Joy M and Sukhatme, Jai (2016) Quasi-geostrophic dynamics in the presence of moisture gradients. In: QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, 142 (694, A). pp. 187-195.

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Official URL: http://dx.doi.org/10.1002/qj.2644

Abstract

The derivation of a quasi-geostrophic system from the rotating shallow-water equations on a midlatitude -plane coupled with moisture is presented. Condensation is prescribed to occur whenever the moisture at a point exceeds a prescribed saturation value. It is seen that a slow condensation time-scale is required to obtain a consistent set of equations at leading order. Further, since the advecting wind fields are geostrophic, changes in moisture (and hence precipitation) occur only via non-divergent mechanisms. Following observations, a saturation profile with gradients in the zonal and meridional directions is prescribed. A purely meridional gradient has the effect of slowing down the dry Rossby waves, through a reduction in the equivalent gradient' of the background potential vorticity. A large-scale unstable moist mode results on the inclusion of a zonal gradient by itself, or in conjunction with a meridional moisture gradient. For gradients that are are representative of the atmosphere, the most unstable moist mode propagates zonally in the direction of increasing moisture, matures over an intraseasonal time-scale and has small phase speed.

Item Type: Journal Article
Additional Information: Copy right for this article belongs to the WILEY-BLACKWELL, 111 RIVER ST, HOBOKEN 07030-5774, NJ USA
Keywords: water vapour; quasi-geostrophy; shallow water; moisture gradients
Department/Centre: Division of Mechanical Sciences > Centre for Atmospheric & Oceanic Sciences
Depositing User: Id for Latest eprints
Date Deposited: 02 Apr 2016 05:20
Last Modified: 02 Apr 2016 05:20
URI: http://eprints.iisc.ac.in/id/eprint/53418

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